The present invention relates to protective packaging cushions that comprise molded foam contained within a bag. More specifically, the invention relates to a machine and method to allow the end-use packager to automatically make such cushions as needed.
The present invention is related to foam-in-place packaging, and offers an alternative to high inventory packaging materials such as corrugated board forms (e.g., cardboard) and premolded polymer (e.g., polystyrene foam) forms.
Foam-in-place packaging is a highly useful technique for on-demand protection of packaged objects. In its most basic form, foam-in-place packaging comprises injecting foamable compositions from a dispenser into a container that holds an object to be cushioned. Typically, the object is wrapped in plastic to keep it from direct contact with the rising (expanding) foam. As the foam rises, it expands into the remaining space between the object and its container (e.g. a corrugated board box) thus forming a custom cushion for the object.
A common foaming composition is formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. The isocyanate and polyol precursors react to form polyurethane. At the same time, the water reacts with the isocyanate compound to produce carbon dioxide. The carbon dioxide causes the polyurethane to expand into a foamed cellular structure, i.e., a polyurethane foam, which serves to protect the packaged object.
In other types of foam-in-place packaging, the foam precursors are injected into a plastic bag which is then dropped into a container holding the object to be cushioned. The rising foam again tends to expand into the available space, but does so inside the bag. Because the bags are formed of flexible plastic, they form individual custom foam cushions for the packaged objects. In several techniques, a specific apparatus is used to make the bag from plastic film while concurrently injecting it with foam. Exemplary devices are assigned to the assignee of the present invention, and are illustrated, for example, in U.S. Pat. Nos. 5,027,583, 5,376,219, and 6,003,288, the contents of each of which are incorporated entirely herein by reference.
Such foam-in-place packaging has gained wide acceptance in many industries. The nature of the technique and the cushions, however, are such that each individual cushion forms a shape that is dictated by a number of variables including the size and shape of the object being packaged, the size and shape of the container, the position of the object in the container, and the placement of the bag in the container before the foam finishes rising. As a resultxe2x80x94and indeed as an advantage in many circumstancesxe2x80x94each foam cushion tends to be a unique customized shape different from almost all other similar cushions. Any cushions that turn out similar or identical do so only by random chance. Accordingly, such random foam-in-place packaging cushions are highly sought after in packaging situations where different objects of different sizes and different shapes must be placed in different boxes on a regular basis. In such circumstances, cushions limited to specific shapes and sizes would represent a disadvantage rather than an advantage.
There are, however, other packaging applications in which similar or identical objects are repeatedly placed in similar or identical orientations in similar or identically sized containers. Such circumstances greatly decrease the need for continuously varying custom cushion sizes, and instead increase the need for more standard packaging elements that have a consistent size and shape.
To date, such standard packaging has been provided by several types of materials. Premolded polystyrene foam is one such common example, as are precut corrugated board (sometimes referred to colloquially as xe2x80x9ccardboardxe2x80x9d), pressed paper, and other similar materials.
Although such materials are quite useful, their precut (e.g. corrugated board) or premolded (e.g. polystyrene foam) nature requires maintaining an inventory of such materials that corresponds to the inventory of items to be packaged. Accordingly, in situations where a large number of objects must be packaged and shipped, a correspondingly large inventory of the packaging cushion materials must be kept in the immediate vicinity. Because the nature of most cushioning materials is such that they have a high ratio of volume to weight, they tend to take up a relatively large amount of space. Thus, such space must be provided and maintained in the immediate vicinity of the objects to be packaged. In a business environment, such inventory space represents a cost. Accordingly, a significant space savings represents a significant cost savings.
U.S. Pat. No. 5,776,510 discloses an apparatus and method for automatically molding defined three-dimensional polyurethane foam cushions utilizing the foam-in-place techniques discussed above, but with added feature of placing a bag containing a foamable composition in a mold as the composition begins to form foam, and maintaining the bag in the mold until the composition has finished forming a foam cushion in a shape conforming to the shape of the mold. This invention has beneficially combined the advantages of on-demand, foam-in-place packaging with the ability to produce standard packaging cushions having a consistent size and shape. However, the inventors hereof have identified several areas where improvement is desired with respect to the apparatus and method disclosed in the ""510 patent.
First, the ""510 patent specifies that the mold is formed of wood. While wood is advantageous in that it is inexpensive and light weight, it is an insulating (as opposed to conductive) material and therefore does not permit the temperature of the mold to be controlled, i.e., by either adding heat to or removing heat from the mold as necessary to maintain the mold at a desired temperature. Typically, the temperature of the mold tends to increase over time in response to consecutive cushionmaking cycles, since the process of making polyurethane foam is generally exothermic. The invention disclosed in the ""510 patent attempts to overcome the inability to control the mold temperature by adjusting the amount of foamable composition dispensed into the bag in response to the changing temperature within the mold. However, varying the amount of foamable composition also varies the cure time for the foam, making it difficult for the operator to know when to remove the cushion from the mold. In addition, the density of the cushions also varies with varying amounts of foamable composition, leading to inconsistent weights and cushioning performance among cushions made in a given mold, which otherwise should be standardized for an intended packaging application.
Secondly, the apparatus disclosed in the ""510 patent has no means for automatically removing the finished foam cushion from the mold. Instead, the cushion must be removed manually by an operator. While the ""510 apparatus provides some assistance to the operator by blowing air into the mold to help release the cushion therefrom, this method has not proven to be sufficiently reliable and efficient for commercial production. Manual removal of the cushions has proven to be excessively slow, often providing a xe2x80x9cbottle neckxe2x80x9d to the production process. In addition, blowing air into the mold is frequently insufficient to release the cushions, causing interruptions in foam cushion production as the non-releasing (i.e., stuck) cushions must be forceably removed from the mold. Further, once the cushions have been removed from the mold, they must be manually moved away from the mold and placed in a designated location for later use, which can further slow the rate of production.
A third area in which improvement of the ""510 apparatus would be desired pertains to the ability of the apparatus to accommodate mold shapes in which the majority of the foam is located on one side of the mold, as opposed to being more uniformly distributed relative to the vertical centerline of the mold. An example of such a mold is a xe2x80x9cCxe2x80x9d shaped mold, in which the hollow portions of the mold, in which the foam is intended to expand, reside primarily to the left of the vertical centerline, with most of the center and right-of-center portions being solid such that virtually no void space exists between the solid portions of the mold and the mold door when the door is closed. When foam is dispensed in the center of such a mold, as is the case with the apparatus shown in the ""510 patent, some or most of the foam is often squeezed out of the sides of the mold when the mold door is closed, resulting in an improperly formed cushion and often a ruptured bag.
Accordingly, a need exists in the art for an improved foam-in-place packaging machine that produces standard packaging cushions having a consistent size and shape, and which overcomes the foregoing limitations of the current machine.
That need is met by the present invention, which provides a machine for forming molded foam cushions, comprising:
a. an apparatus for enclosing a foamable composition in a flexible bag;
b. a mold having a cavity and a closure mechanism and being movable between an open position and a closed position such that, when in the closed position, the closure mechanism and the cavity define an enclosed three-dimensional shape, the mold comprising a material capable of transferring sufficient heat to or from the cavity to maintain the cavity at a desired temperature;
c. a device for controlling the temperature of the mold cavity;
d. means for placing the bag in the mold cavity while the mold is in the open position, whereby, when the mold assumes the closed position, the foamable composition expands within the cavity to form a foam cushion that substantially conforms to the three-dimensional shape; and
e. means for pulling the foam cushion from the mold cavity.
The invention also provides a method for forming molded foam cushions, comprising:
a. enclosing a foamable composition in a flexible bag;
b. placing the bag in a cavity of a mold, the mold comprising a material capable of transferring sufficient heat to or from the cavity to maintain the cavity at a desired temperature, the mold further including a closure mechanism, the mold being movable between an open position and a closed position such that, when in the closed position, the closure mechanism and the cavity define an enclosed three-dimensional shape;
c. closing the mold as the foamable composition begins to expand in the bag so that the composition forms a foam cushion that substantially conforms to the three-dimensional shape of the mold;
d. controlling the temperature of the mold cavity to provide a desired cavity temperature during the formation of the foam cushion; and
e. opening the mold and pulling the foam cushion from the cavity.